As one method for the shielding of electromagnetic waves of printed circuit boards, a process for producing a printed circuit board which can mainly shield electromagnetic waves generated therefrom in a simple manner has conventionally been proposed in which a printed circuit pattern is formed by an ordinary printed circuit pattern-forming technique, an insulating layer is formed thereon over an area to be shielded, and an electrically conductive layer is then further formed thereon. In this process, the electrical insulating layer is formed by coating, printing, or otherwise applying an insulating layer-forming coating fluid and then curing the coating. However, since the copper foil pattern projects from the substrate surface, the insulating layer has a reduced thickness at portions thereof which are located on edges of the copper foil line constituting the printed circuit patterns. Therefore, formation of an electrically conductive layer which is to be a ground on such a thin insulating layer results in a reduced distance between the signal lines in the printed circuit and the ground, so that high-frequency waves tend to leak out to the ground line and, in the worst case, the result is virtually the same as an open circuit between the printed signal lines and the ground.
On the other hand, resistor-possessing printed circuit boards are produced by forming carbon resistors or the like on printed circuit boards by means of a screen printing technique, etc. In this process, a resistor ink is printed and then cured, and the resistance value is regulated by trimming, etc. Omitting this trimming step or greatly reducing the time required for this step is desirable in that production efficiency can be increased and cheaper printed circuit boards with resistors can be provided. However, it has been extremely difficult for conventional printed circuit boards to be uniformly printed with a resistor ink or the like at a desired thickness and width, since for forming a resistor, the ink should be printed on a printed circuit board's surface including gaps between the insulating substrate surface and the surface of the projecting conductor.
A multilayered printed circuit board is produced by using a printed circuit board as an inner or intermediate lamina prepared by forming a desired printed circuit pattern on a completely cured copper-clad laminate. In this process, it is necessary to use an adhesive prepreg with a prescribed impregnating resin flow in an amount about two times the desired amount, in order to completely fill the space between inner-lamina printed circuit conductors and to maintain a sufficient distance between adjacent printed circuit conductors thereby to ensure reliability. Further, according to the configuration of the printed circuit pattern, vacuum laminating is indispensable for avoiding void formation, etc. Due to these limitations, there has been a disadvantage that the conventional multilayered printed circuit board has an increased printed circuit layer distance and, as a result, thick multilayered boards can only be produced.
As methods for mounting chip devices on a printed circuit board, the following have been used. In the case of chip devices having a small number of pads, such as a resistor, capacitor, or diode, there has been a method in which a solder paste, for example, is printed or otherwise applied beforehand in a predetermined position, and the chip devices are placed thereon and the solder or the like is then melted to fix the chip devices. In the case of chip devices having a relatively large number of pads to be connected, there has, for example, been employed a method in which the chip devices are fixed to a predetermined position by means of a quick-curing adhesive or the like according to need and then secured by soldering. However, chip devices of the former type are rapidly coming to be small-sized and micro devices of about 1 mm or smaller are produced in an increasing quantity, so that fixing of such chip devices in predetermined positions is becoming difficult.
On the other hand, attention is now focused on the production of laminates by a continuous process which is intended mainly to improve the laminate production efficiency. It is necessary for this process to complete laminating within a short pressing time. However, the laminates produced by such a process, in which prepregs used in conventional daylight pressing or prepregs obtained by adding a large amount of a catalyst, etc., to such conventionally used prepregs are employed and they are completely cured by short-time pressing with the heating temperature or other conditions being changed, have the defect that the chemical resistance and other properties are inferior to the laminates produced by conventional/daylight pressing.